This application is based on and claims benefit of priority of Japanese Patent Application No. 2000-048272 filed Feb. 24, 2000, the contents of which are incorporated hereinto by this reference.
1. Field of the Invention
The invention relates to an airbag device with an airbag. A coating agent is coated on the airbag so as to inhibit leakage of an expansion gas made to inflow. In particular, the invention relates to an airbag device, in which an airbag can ensure a predetermined or higher inner pressure value during a predetermined time while a coating agent is held down in coating amount. The airbag device includes, for example, a head protective airbag device mounted on a motorcar, an airbag device for lateral collision and mounted on a seat, and the like.
2. Description of Related Art
Conventionally, for example, with a head protective airbag device, an airbag is folded and received to extend over a pillar section and a roof-side rail section on a peripheral edge of an opening on a door on a vehicle-interior side and windows. When an expansion gas is made to flow into an airbag from an inflator for expansion, the airbag is developed and expanded in a manner to cover the opening (Japanese Patent Laid-Open No. 321535/1999).
Also, it has been demanded that with this kind of airbag device, an airbag maintain inner pressure of 10 KPa or higher during about three seconds after the beginning of inflation taking account of turning-sideways of a vehicle.
Therefore, airbags have been manufactured not by sewing but by double-weaving so as to enable inhibiting leakage of an expansion gas having inflowed. Further, a coating agent of silicone rubber is coated on surfaces of an airbag.
Furthermore, it has been contemplated to increase inner pressure values before and after the completion of expansion of an airbag (after about 25 ms lapses since the beginning of inflation), that is, peak inner pressure values of the airbag so that the airbag can maintain inner pressure of 10 KPa or higher during about three seconds after the beginning of inflation. The reason for this is that with high peak inner pressure values, the airbag is believed to be capable of maintaining inner pressure of 10 KPa or higher during about three seconds after the beginning of inflation even when inner pressures in the airbag decrease due to leakage of an expansion gas.
When an airbag becomes high in peak inner pressure values, however, inner pressure values in some cases decrease conversely after three seconds since the beginning of inflation. The reason for this appears that a weaving pattern of an airbag in double-weaving is influenced by high peak inner pressure values to cause widening of texture, thus generating gas leakage.
In order to cope with this, it is conceivable to further increase an amount of a coating agent being applied to an airbag. However, an increased coating amount will lead to an increase in weight of an airbag. Thus this is contrary to the demand for mounting a lightened airbag device on a vehicle.
An object of the invention is to solve the above-mentioned problems and to provide an airbag device, in which a coating agent is held down in amount of coating and an airbag can maintain inner pressure of a predetermined value or more during a predetermined time after inflation.
The above-mentioned object can be attained by an airbag device according to a first embodiment of the present invention. The airbag device is provided with an airbag, which is folded for receipt in a vehicle in a manner to permit an expansion gas from an inflator to flow thereinto to develop and expand the airbag, which airbag is formed by means of double-weaving, and on which a coating agent of silicone rubber for preventing leakage of the expansion gas through texture is coated. In the airbag, average values of the number of warps and wefts per square inch in double-weaving are 49 to 50 for the first embodiment. With the airbag, peak inner pressure values before and after completion of expansion are set corresponding to the coating weight of the coating agent to be on the basis of a straight line (referred to below as a first boundary line) represented by a straight-line formula (Y=5X/2xe2x88x92100) for a relationship between peak inner pressure values and the coating agent at the time of inflowing of the expansion gas, where in the system of XY coordinates peak inner pressure values (KPa) are indicated by X and the coating weight (g/m2) of the coating agent is indicated by Y, and in the ranges (referred below to as a first boundary range) of 70 KPa or higher and 80 to 155 g/m2 in a leftside region including values on the straight line.
In the airbag device of the first embodiment, peak inner pressure values are set in accordance with the coating weight of the coating agent. For example, in the case where minimum inner pressure values (referred below to as preserving minimum inner pressure values) for about three seconds after inflation is started are 10 KPa or less, peak inner pressure values are decreased in the first boundary range so as to suppress influences of the peak inner pressures. Such corrective action can be performed as by changing the inflator into one having a small output and by increasing a volume of the airbag, into which the expansion gas is caused to flow.
In the airbag of the first embodiment, in which average values of the number of warps and wefts per square inch in double-weaving are 49 to 50, preserving minimum inner pressure values of 10 KPa or higher can be ensured by setting of peak inner pressure values within the first boundary range in accordance with the coating weight of the coating agent in the first boundary range.
Incidentally, preserving minimum inner pressure values of 10 KPa or higher can be ensured in the rightside region with the first boundary line as a standard by increasing the coating weight of the coating agent. In this case, however, the coating agent will be increased in coating amount to lead to an increase in weight of the airbag, and waste of the coating agent is caused.
Also, since the coating weight of the coating agent in the first boundary range is 155 g/m2 or less according to the invention, the coating agent being applied to the airbag can be held down as much as possible.
In addition, if the coating weight of the coating agent is less than 80 g/m2, a sealing quality at the completion of expansion of the airbag cannot be ensured so preservation of inner pressures thereafter cannot be expected.
Also, if peak inner pressure values are less than 70 KPa, the cover covering the folded airbag cannot be moved, which is not practical.
Accordingly, with the airbag device of the first invention, the coating agent is held down in amount of coating and the airbag can maintain inner pressure of 10 KPa or higher during three seconds after inflation.
Also, the above-mentioned object can be attained by an airbag device of a second embodiment of the present invention. The airbag device of the second invention is provided with an airbag, which is folded and received in a vehicle in a manner to permit an expansion gas from an inflator to flow thereinto to develop and expand the airbag, which airbag is formed by means of double-weaving, and on which a coating agent of silicone rubber for preventing leakage of the expansion gas through texture is coated. In the airbag, average values of the number of warps and wefts per square inch in double-weaving are 51 or more. With the airbag, peak inner pressure values before and after completion of expansion are set corresponding to the coating weight of the coating agent to be on the basis of a straight line (referred to below as a second boundary line) represented by a straight-line formula (Y=5X/2xe2x88x92150) for a relationship between peak inner pressure values and the coating agent at the time of inflowing of the expansion gas, where in the system of XY coordinates peak inner pressure values (KPa) are indicated by X and the coating weight (g/m2) of the coating agent is indicated by Y, and in the ranges (referred below to as a second boundary range) of 70 KPa or higher and 80 to 155 g/m2 in a leftside region including values on the straight line.
In the airbag device of the second embodiment, peak inner pressure values are set in accordance with the coating weight of the coating agent in the same manner as in the airbag device of the first invention. For example, in the case where preserving minimum inner pressure values for about three seconds after inflation is started are 10 KPa or less, peak inner pressure values are decreased in the second boundary range so as to suppress influences of the peak inner pressures. Such corrective action can be performed as by changing the inflator into one having a small output and by increasing a volume of the airbag, into which the expansion gas is caused to flow.
In the airbag, in which average values of the number of warps and wefts per square inch in double-weaving are 51 or more, preserving minimum inner pressure values of 10 KPa or higher can be ensured by setting of peak inner pressure values within the second boundary range in accordance with the coating weight of the coating agent in the second boundary range.
Incidentally, preserving minimum inner pressure values of 10 KPa or higher can be ensured in the rightside region with the second boundary line as a standard by increasing the coating weight of the coating agent. In this case, however, the coating agent will be increased in coating amount to lead to an increase in weight of the airbag, and there is caused waste of the coating agent.
Also, the coating weight of the coating agent in the second boundary range is 155 g/m2 or less. Therefore, the coating agent being applied to the airbag can be held down as much as possible.
In addition, the reason why the coating weight of the coating agent is 80 g/m2 or more and peak inner pressure values are 70 KPa or more is the same as that for the airbag device of the first embodiment.
Also, the airbag device of the second embodiment has a high weaving density as compared with the airbag device of the first embodiment. Therefore, peak inner pressure values can be set high in the airbag device of the second embodiment. Setting of high peak inner pressure values in the second boundary range makes it possible to shorten the time elapsed until expansion of the airbag is completed.
Accordingly, with the airbag device of the second embodiment, the coating agent is held down in amount of coating and the airbag can maintain inner pressure of 10 KPa or higher during three seconds after inflation. Further, it is possible to shorten the time elapsed until expansion of the airbag is completed.